OH overtone bands and potential energy curves of the hydrogen-bonded formic and acetic acids

The absorption spectra of formic and acetic acids and acetic acid-d in pure liquid and of their carbon tetrachloride solutions were measured in the 3850–15400 cm⁻¹ region. The higher overtone bands of the hydrogen-bonded OH stretching vibrational mode for the chain polymer of formic acid (in the pure liquid) and for the cyclic dimer of formic acid (in the carbon tetrachloride solution) or acetic acid were observed at 5450 ± 200, 6000 ± 150, 7850 ± 150, 9700 ± 200, and possibly 12000 ± 300 cm⁻¹ and at 5350 ± 200, 5900 ± 150, 7750 ± 150, 9500 ± 200, and 11300 ± 300 cm⁻¹, respectively, having broad half-widths (500–600 cm⁻¹) and submaxima as in the gaseous state. The 5450 and 7850 cm⁻¹ bands of the chain polymer and the 5350, 7750 and 11300 cm⁻¹ bands of the cyclic dimers were first observed by the present study. With the aid of the observed frequencies, we determined the asymmetrical or symmetrical double minimum potential energy curve with a Gaussian barrier of 0.82 ∼ 0.88 eV or 0.80 ∼ 0.86 eV, respectively.     

Understanding the complexation of aliphatic and aromatic acids guests with octa acid

In this study, inclusion of 10 guest molecules, adamantyl and naphthyl carboxylic acids with different structural and electronic properties, within a synthetic cavitand octa acid was probed by isothermal calorimetry, 1D and 2D ¹H nuclear magnetic resonance spectroscopy, and molecular dynamic simulations. Under the condition of the experiments (pH ~ 8.7), the guests were included as carboxylate anions with the polar anionic head group facing water and hydrophobic carbon skeleton buried within the cavitand, forming 1:1 host to guest complexes. Importance of weak interactions between the guest and the cavitand interior is reflected in the measured negative ΔH values. Although ΔH was negative for all guests, ΔS was positive for adamantyl guests and negative for naphthyl guests. Quite likely the difference in hydrophobicity between the 2 sets of molecules and the strength of interaction between the guest and the host are responsible for the sign difference in ΔS between the 2 series. The importance of steric factor during inclusion of naphthyl carboxylic acids within octa acid cavity is brought out by the difference in thermodynamic parameters between the 1‐ and 2‐substituted naphthyl carboxylic acids; 2‐naphthyl carboxylic acids that can penetrate deeply have larger ?ΔH and 1‐naphthyl carboxylic acids that can only enter the cavity in an angle have smaller ?ΔH. As expected, based on the well‐known concept of “enthalpy‐entropy compensation,” the molecules that have large ?ΔH are accompanied by large ?ΔS.     

Correlations between Moelwyn–Hughes parameter, available volume and intermolecular free-lengths in liquid systems

Thermo-acoustical parameters of liquid mixtures viz., Acetone, Methyl Iodide and Acetone + Methyl Iodide have been evaluated at different temperatures in terms of the coefficient of volume expansion, on the assumption that the Moelwyn–Hughes parameter has been utilized to establish some simple relations between the lattice Gruneisen parameter, Beyer's non-linearity parameter, the Anderson–Gruneisen parameter and the Sharma constant. A relationship among the isobaric, isothermal and isochoric microscopic (lattice) Gruneisen parameters have been studied and analysed in the case of liquid mixtures. The Sharma's parameter S₀ remains invariant with the temperature over a wide range of temperatures and retains its characteristics value i.e., 1.11 ± 0.01 as observed in case of liquid systems. The present treatment has the distinct advantage of calculating available volume (V_a) and intermolecular free-length (L_f) through Moelwyn–Hughes parameter mainly. Analysis of such type is not found so far in literature.     

On the origin of the additional bands observed in the photoelectron spectra obtained with Ne or Ar resonance lines

Photoelectron spectra of benzene, fluorobenzene and pyridine ionized by the Ne (16.85 and 16.67 eV) or by the Ar (11.83 eV and 11.62 eV) resonance lines are reinvestigated with a spherical-grid kinetic energy analyzer. Some other hydrogenated and non-hydrogenated molecules are also studied. In the spectra of the hydrogenated molecules a band not observed with the He I (21.22 eV) resonance line is generally visible. It is shown that this additional band can be interpreted as being due to the Lyman α line (10.195 eV). Hydrogen coming from the target molecules is probably responsible for the occurrence of this impurity line.     

Bogoliubov shadow bands in the normal state of superconducting systems with strong pair fluctuations

On the basis of a scenario where electron pairing is induced by resonant two-particle scattering (the boson-fermion model), we show how precursors of the superconducting state-in the form of overdamped Bogoliubov modes-emerge in the normal state upon approaching the transition temperature from above. This result is obtained by a renormalization technique based on continuous unitary transformations (the flow equations), projecting out the coherent contributions in the electron spectral function from an incoherent background.     

O3与O3分子间相互作用的理论研究

采用从头算方法,在B3LYP水平下对O3分子单体及其二聚体进行了几何结构优化,得到四种O3分子二聚体的稳定构型,并经MP2法、均衡法(Massage)分别校正了电子相关和基组叠加误差(BSSE),通过对分子中原子间的最短距离,分子间质心距离与各构型相互作用能的关系进行了分析、比较,得到了最稳定的构型,其对应的O3分子二聚体相互作用能为:-8.788 kJ/mol.     

Comparison between standard and counterpoise-corrected optimization using some hydrogen and halogen bonded systems

The effect of the counterpoise correction on the geometries, stabilization energies, and vibrational harmonic frequencies of some hydrogen- and halogen-bonded systems (B?=?CH₃CN,?HCN,?NH₃,?N₂,?CO,?H₂O,?H₂S,?PH₃;?HX?=?HF,?HCl,?HBr,?HCN,?HCF₃; XY?=?Br₂,?BrCl,?BrF,?Cl₂,?ClF,?F₂) has been analysed at the MP2 level of theory using the popular 6-311++G(d,p) basis set. The optimized B?···?H and B?···?X bond lengths increase with counterpoise (CP) correction. In some cases standard values and in other cases CP-corrected values are close to experimental data. The absolute values of complexation energies of CP-corrected structures are higher than standard by inclusion of BSSE correction. The effect of CP correction on intermolecular bond lengths and complexation energies of B?···?XY series are usually higher than B?···?HX. Also, this effect is higher for H₂S and PH₃ groups. The CP correction changes the vibrational harmonic frequencies by 0–100%. The changes are frequently lower than 20% for frequencies higher than 300?cm^?1.     

Structure and reactivity in the hydrolyses of aliphatic carboxylic acid esters and chlorides

For hexanoic acid and its seven isomers, relative rates have been determined for acid catalysed esterification with methanol, and compared with those for saponification of the methyl esters. A good correlation between logarithms of relative rates for the two reactions is obtained, and it is suggested that the eight isomers provide a test set of compounds in which steric effects alone act on reactivity at the acyl carbon. A full set of steric parameters ( values) are presented. Rates of solvolyses of the acid chlorides of the isomers have been determined conductometrically in 3:1 wt:wt acetonitrile water. Logarithms of relative rates show a poor correlation with , and, taking into account the solvent dependence of the rates, the pattern excludes both rate‐limiting formation of a tetrahedral intermediate and rate‐limiting dissociation of chloride to form acylium ions. The remaining possibilities, a concerted process (A_ND) and rapid reversible formation of a hydrate followed by rate‐limiting dissociation of chloride (A_N + D) are considered. Copyright © 2007 John Wiley & Sons, Ltd.